In the manufacture of synthetic-resin foils or sheet (plastic) bags, the synthetic-resin material is usually blown to produce a foil or sheet which is flattened and sealed along various edges to provide the individual bags which can be separated from the continuous extruded material and packaged or assembled for distribution or use.
One of the principal forms of distribution is an assembly of such bags in a stack in which the bags are interconnected along, say, one edge, i.e. in a pad or block from which individual bags can be removed for use. A stack of bags can also be subdivided to form two or more blocks or pads and the blocks or pads can be wrapped, attached to a support or otherwise processed following assembly of the bags.
In order to stack the individual bags and join the stacks of bags, apparatus has been proposed to be provided downstream of the automatic bag-making machinery so as to constitute part of the automatic or assembly line production of padded bags.
The padding or stacking machinery can comprise a stacking surface upon which the bags are accumulated and which can be formed with or can be associated with an abutment or stop for the leading edge of the bags emerging at high speed from the bag-making machine, a padding press for joining the bags of a stack together, means for carrying away the pad or stack of interconnected bags, and a discharge device for the stack of interconnected bags.
In such systems, the conveyor is usually a belt conveyor which is operated periodically in accordance with a particular cycle, usually in the cadence of the press operation so that a stack of nonconnected bags is introduced into the press, the press is closed to bind the bags of the stack into connected or padded relationship, and the press is then opened for the conveyor to carry away the resulting pad or block.
In the press the interconnection of the bags can be effected by edge-welding or heat-sealing or by any other sealing technique which may take place concurrently with further processing in or adjacent the press. Such further processing can include, in addition to the steps previously mentioned, the formation of holes in the pad or block to enable the latter to be hung up, a subdivision of the stack or block into two or more pads or blocks, etc. the processing can be carried out with tools movable independently of the press or associated therewith.
A block-forming or bag-stacking machine for these purposes is described, for example, in the German patent document (Auslegeschrift) DE-AS 23 02 477. In this system, the press is mounted upon a carriage which is movable along with the conveyor and counter thereto so that the press can be brought into the region in which the bags are initially stacked. In other words the bags are stacked within the open press. When a given number of bags have been accumulated, i.e. the stack has reached the desired height and number of bags, the press is closed and the press is displaced with the pad during the interconnection of the bags via the conveyor belt, past whatever stationary processing tools may be required to act upon the stack, toward the discharge side of the machine. The press is then opened and the pads or blocks discharged. The press is then returned to the stacking side of the machine.
In practice, this system has been found to be comparatively slow since the press has a large inertial mass which can only be moved slowly and which cannot be accelerated or decelerated rapidly in a convenient manner.
Furthermore, while the press is not at the stacking location, the stacking of the bags must be interrupted. This is done in conventional systems by programming the bag-producing machine to have a certain number of nonproductive cycles corresponding to the time required for return of the press to the stacking location. In my experience ten or more such nonproductive cycles of the bag-producing machine must be provided for each pad or block to be produced.
A further disadvantage of this earlier system is that the stop or abutment for the leading edge of the bags is provided in the press which makes it difficult to remove improperly oriented bags or to have access to the stack during the stacking process in a convenient manner.
Mention should be made of the fact that in the paper and printing industries it is known to assemble or collate paper sheets or signatures to so-called stacks upon stacking surfaces having a grill between the bars of which a member can engage to move the stack. Reference may be had in this connection to U.S. Pat. No. 3,298,683. In this system, a pair of grill-shaped supports are required to displace the stack.
Reference may also be had to the German patent document (Auslegeschrift) DE-AS 20 04 334 in which the stack-receiving system can be raised and lowered and in which an array of bars can be provided as the receiving surface, the latter being drawn away from the stack.
In both these prior art devices described there is a relative movement along the plane of the receiving surface between the bars thereof and the stack when the stack is removed from the surface or the surface withdrawn from beneath the stack.
While this relative movement has little effect upon signature stacks and stacks of paper, it constitutes a barrier to the use of these techniques in the handling of plastic bags whose adhesion to one another is generally less than that between the lowermost bag and the bars upon which the stack is formed.
As a result, the relative movement gathers the lowermost bags and thereby disrupts the stack.
In German patent document (Auslegeschrift) DE-AS 23 02 477, however, this problem does not arise although it is essential to move the press or its carriage with the disadvantages enumerated above.
In general, therefore, it may be said that stacking techniques which have found prominence in the paper, printing, collating and bookbinding fields, in the assembly of stacks of interconnected leaves, cannot be used effectively in the formation of stacks, pads or blocks of plastic bags and, concomitantly these techniques for high speed stacking in the paper art cannot be used to advance techniques current in the art of stacking of plastic bags without introducing new disadvantages in this latter field.